1. Field
The present application relates generally to the operation of power distribution systems, and more particularly, to methods and apparatus for time synchronization and measurement of power distribution systems.
2. Background
The electricity industry is going through a metamorphosis with utilities rolling out what is known as the “Smart Grid”. The “Smart Grid” is an intelligent, managed, controlled, network communication overlay on top of the existing electric distribution network. Essentially the Smart Grid links utility computer servers to grid infrastructure devices and new “smart electricity meters.” Several Smart Grid services require that precise time be known. For example, synchronized phasor measurements (time-stamped measurements of alternating current phase), Time of Use (TOU) metering, and scheduled load shedding are just a few of these services.
However, determining precise synchronized time across the smart grid can be challenging and expensive. Some higher end utility infrastructure components use Global Positioning System (GPS) modules to maintain precise time, but these modules are too expensive to be deployed in individual smart meters. Thus, smart meters must use other, less accurate and less expensive, means of acquiring and maintaining time.
Typically, smart meters use the power line frequency itself to measure the passing of time, filling in with expensive real-time clock components to cover power outages. Unfortunately, this adds significant cost to the meter, and time accuracy errors tend to accumulate over periods of usage. The result is that time in smart meters is nowhere near accurate enough to enable synchronized phasor measurements, and it is barely adequate for Time of Use metering.
Therefore, it would be desirable to have a simple cost effective mechanism that operates to provide time synchronization and measurement for improved monitoring and failure detection for power distribution systems.